Gene therapy is one of the fastest growing areas in experimental medicine. However, most studies are only Phase I or Phase II clinical studies designed mainly to evaluate the toxicity of the viral vectors and constructs being used. A major drawback has been the design of vectors that are both safe and efficacious. Recent efforts in the field have been directed toward the use of retroviral vectors and viral vectors pseudotyped with glycoproteins from highly virulent viruses such as filoviruses.
Retroviruses are ribonucleic acid (RNA) viruses that include an RNA genome enclosed within a viral capsid wherein the capsid is surrounded by an envelope, or lipid bilayer. Glycoproteins present in the lipid bilayer interact with receptors on the surface of various host cells and allow the retroviruses to enter the host cell. Once in the cell, the retroviruses reverse transcribe the RNA of the viral genome into a double-stranded DNA and incorporate the DNA into the cellular genome as a provirus. Gene products from the integrated foreign DNA may then be produced so that progeny viral particles may be assembled. As retroviruses can be modified to carry exogenous nucleotide sequences of interest, such recombinant retroviruses have a variety of uses. For example, such recombinant retroviruses are important in introducing desired exogenous sequences into a cell, so that relatively high levels of the protein encoded by the sequences may be produced. However, use of such recombinant retroviruses has several drawbacks.
One such drawback is that retroviruses do not have a broad host range. Efforts at increasing the host range of retroviruses have included substituting the envelope glycoproteins of the retrovirus with that of a different virus, thus forming a pseudotyped retrovirus. The pseudotyped retrovirus advantageously has the host range of the different virus. However, some retroviruses have been pseudotyped with viral glycoproteins that are toxic to cells, so the cells can only produce the virus for a limited time. Furthermore, in many cases, the pseudotyped retroviruses cannot be stably produced and may not be produced at a high titer. Stable cell lines have been developed to overcome the toxicity problems and to stably produce such pseudotyped retroviruses. However, there still exists a need for pseudotyped retroviruses that will allow for the production of high titers that would be required for routine gene transfer and/or gene therapy.
Thus it would be desirable to have a pseudotyped retrovirus that is not toxic to cells and produces high titers of a competent virus. It would also be desirable to have a cell line to produce such retroviruses. Methods for using such a virus would also be desirable.